The Probability Scale
Impossible
0
Unlikely
Even Chance
0.5 or 1/2
Likely
Certain
1
Calculating Probability
The probability of an event is calculated with this formula:
P(event) = Number of favourable outcomes / Total number of possible outcomes
For example, the probability of rolling a 4 on a standard six-sided die is 1/6, because there is one '4' and six possible outcomes in total.
Probability Practice 🎲
1. A bag contains 5 red marbles, 3 blue marbles, and 2 green marbles.
a) What is the probability of pulling out a blue marble?
b) What is the probability of pulling out a red marble?
c) Is it more likely to pull a red or a blue marble?
2. You spin a spinner with 8 equal sections numbered 1-8.
a) What is the probability of landing on an even number?
b) What is the probability of landing on a number greater than 5?
3. Mark the following events on the probability scale below.
A) You will have homework this week.
B) A coin flip will land on heads.
C) It will snow in Auckland in July.
📚 NZ Curriculum Alignment
Mathematics & Statistics
Achievement Objective: S4-1
Plan and conduct investigations using the statistical enquiry cycle
Key Competencies
- • Thinking critically about probability concepts
- • Using mathematical language and symbols